Method for eliminating halogenated and non halogenated waste

ABSTRACT

Disclosed is a method for eliminating halogenated and non halogenated waste, whereby waste is reacted with products containing metal oxide in an oxygen-free medium at temperatures ranging from  800 ° C. to  1100 ° C.

[0001] The present invention relates to a process for disposing ofhalogenated and non-halogenated waste substances.

[0002] Substituted, in particular halogenated hydrocarbons, such as arepresent for example in carbon tetrachloride, chloroform, methylenechloride, tetra- and trichloroethylene, tetrachloroethane, PCB etc., butalso in PVC or polyvinylidene chloride, are a more or less problematicaltoxic or special waste following use, which has to be disposed of.

[0003] Substances with a strong toxic effect on the environment and man,such as halogenated compounds, in particular polyhalogenated substancessuch as PCBs or TCDD/TCDF (dioxins/furans) cannot be automaticallyrecycled and have to be disposed of in an environmentally friendlymanner.

[0004] The disposal takes place either by dumping or by incineration onthe high seas or else on land in high-temperature furnaces with anexcess of air.

[0005] The energy requirement is in many cases not inconsiderable, sincenot only do the substances to be disposed of have to be vaporised andheated to the required decomposition temperature, but enormous amountsof air also have to be heated up. In so doing either, as withincineration on the high seas, pollution of the atmosphere and the riskof acid rain have to be allowed for, or extremely expensive plants arerequired for keeping the air clean.

[0006] There is known from DE-A-33 13 889 a process or an apparatus fordisposing of toxic and special waste, in which the toxic wastesubstances are mixed with an electrically conductive material, inparticular in the form of iron powder and/or coke, and are brought in aninduction furnace to the decomposition temperature of the toxic and/orspecial waste to be eliminated.

[0007] U.S. Pat. No. 4,435,379 discloses a process for decomposingchlorinated hydrocarbons with metal oxides with the aim of convertingall carbon atoms into carbon monoxide. It is a question here ofproviding elemental chlorine for the conversion of hydrogen groups intoHCl. The overall ratio of chlorine to hydrogen groups must be at least1:1 here, in order to be able to produce metal chloride.

[0008] U.S. Pat. No. 4,587,116 discloses a similar process, in whichnitrogen-containing waste substances can also be disposed of. Theheating likewise takes place from the outside and not from the inside.

[0009] EP-0 306 540 discloses a process for recovering energy fromsubstituted hydrocarbons such as are present e.g. as CCl₄, CHCl₃,C₂H₂Cl₄, PCB, PVC, polyvinylidene chloride etc. in pure or bound form.In this process the waste material is decomposed thermally in aninductively heated reactor in the presence of a barely treatable metaloxide and an electrically conductive material, for example electrodecoke or electrographite, and in contact with water vapour attemperatures of between 800 and 1100° C. A portion of the metal oxidethat corresponds to the chloride content of the waste materials is thereconverted into volatile metal chloride. A portion of the liberatedcarbon is converted into carbon monoxide and the portion of the carbonnot reacting on the metal oxide is converted to water gas (CO+H₂) withthe aid of a stoichiometric amount of water vapour.

[0010] It is the object of the present invention to develop a processwhich makes it possible to dispose of various halogenated andnon-halogenated waste materials in an environmentally friendly manner.

[0011] This object is achieved according to the invention by a processfor disposing of halogenated and non-halogenated waste materials inwhich the halogenated and non-halogenated waste materials are reactedwith metal oxide-containing products with the exclusion of oxygen attemperatures of 800° C. to 1100° C.

[0012] The process described here can be used for the environmentallyneutral recycling of halogenated and non-halogenated waste materials.

[0013] The volume of the wastes used is largely reduced, so that as fewresidues as possible remain and as large a quantity as possible ofmetals/metal compounds is obtained. As positive an energy balance aspossible is aimed at during the reaction.

[0014] In a preferred embodiment of the process, carbon-containinghalogenated waste materials are reacted.

[0015] In an advantageous embodiment of the process, carbon dioxide isadded as a fluidising gas.

[0016] Furthermore the reactor can also be supplied with carbon in theform of graphite and/or coal.

[0017] In a preferred manner a halogenatable metal oxide-containingproduct is used as a metal oxide-containing educt.

[0018] In a specific embodiment variant of the process according to theinvention products which contain CaO, TiO₂, SiO₂, Al₂O₃ and/or Fe₂O₃ ora mixture thereof are used as halogenatable, metal oxide-containingreactants.

[0019] Various metal-oxide containing waste materials, such assilicon-containing residues from the metal-working industry, filterdusts, flue ashes, wind-blown sands, waste dumps, galvanic sludges,slags, slate residues etc., can also serve as reactants. Simple quartz,which consists about 98% of silicon dioxide (SiO₂), is the simplestpossible material which can be use for the conversion.

[0020] All of the above-mentioned materials are characterised by thefact that they contain a relatively high content of halogenatable metaloxides (CaO, SiO₂, TiO₂, Al₂O₃, Fe₂O₃ etc.

[0021] This has the resultant advantage that materials containing metaloxides not treatable with economic agents to date now acquire a usefulapplication.

[0022] Solvents such as carbon tetrachloride, chloroform, methylenechloride, tetra- and trichloroethylene, tetrachloroethane, coolants orrefrigerants, PCB, pesticides, fungicides and herbicides, halogenatedplastics such as PVC can be used as halogenated waste materials.

[0023] A portion of the metal oxide that corresponds to the chlorinecontent of the waste materials is converted into metal chloride by theabove-mentioned process. Ecologically and economically useful metalchlorides are obtained, wherein silicon and titanium tetrachloride(SiCl₄, TiCl₄,) represent particularly preferred products.

[0024] Other materials such as spent oils, lubricants, fats, paints,dyes, tars, waxes, plastics, coolants and solvents, brake fluid orsimilar non-halogenated substances and materials can also be disposedof.

[0025] The reaction or conversion products preferably formedthermodynamically under these process parameters are hydrogen (H₂),which primarily occurs in gaseous form, together with smaller volumes inpercentage terms of methane (CH₄).

[0026] The formation of environmentally dangerous or environmentallypolluting, gaseous substances such as carbon monoxide (CO), as well asthe carbon dioxide (CO₂) known as a so-called greenhouse gas, is, underthe preferred reaction conditions, negligibly small. Only attemperatures above 1100° C. can CO or CO₂ be formed by chemicaldecomposition processes.

[0027] The conversion takes place in a fluidised bed reactor. The lattercan be constructed either from special ceramics, silicon carbide (SiC)or specially alloyed steels.

[0028] The reactor can be brought to the required operating temperatureseither by the use of electric heating elements (e.g. heatinghalf-shells) or by the use of an induction heater. The temperaturesrequired for the conversion lie in the range from 800° C. to 1100° C.The reaction itself takes place with the exclusion of oxygen. Carbondioxide (CO₂) is used as the fluidising gas.

[0029] The halogenated compounds are decomposed into their simplestconstituents by the high temperatures. In the case of chlorinatedhydrocarbons, hydrogen chloride, hydrogen, alkanes and chlorine gas areformed. The chlorine gas and the hydrogen chloride serve as chlorinatingagents for the metal oxide-containing products or wastes. Products ofthis chlorinating reaction are the thermodynamically preferred metalchlorides.

[0030] In addition to the chlorides, hydrogen and carbon monoxide areformed, which can be used as a synthesis gas either for the obtaining ofelectrical energy or for other chemical syntheses, for example themethanol synthesis.

2H₂+CO═CH₃OH

[0031] Reaction Equation

[0032] The carbon dioxide (CO₂) used as the fluidising gas is convertedcompletely to carbon monoxide (CO) by reaction with the carbon of thedecomposed hydrocarbons and by an additional coal or graphite charge inthe top part of the reactor.

[0033] The so-called BOUDOUARD reaction is referred to in this context:

CO₂+C=2 CO

[0034] Reaction Equation 2

[0035] The formation of environmentally harmful compounds such asdioxins, furans or e.g. phosgene (COCl₂) is extremely improbable underthe prevailing reaction conditions.

[0036] All the halogenated metal compounds produced are presentinitially in gaseous form. Depending on the starting material, solid,i.e. crystalline metal compounds can be obtained by cooling to roomtemperature, or else liquid metal compounds by condensation at lowtemperatures.

[0037] The degree of purity of these compounds is around 96% and can befurther improved e.g. by a fractionating distillation, also calledrectification.

[0038] Various embodiments of the invention will now be described belowby means of the attached figures, where

[0039]FIG. 1 shows a diagram of the plant for disposing of halogenatedwaste materials.

[0040] In the diagrammatic flow-chart of the process, as shown in FIG.1, a feed line 1 for the halogenated waste materials, a feed line 2 formetal oxide-containing products, and a line 3 for the discharge ofunconverted materials 3 can be seen. A fluidising gas (CO₂) is blowninto the fluidised bed reactor 5 via a feed unit 4.

[0041] The reactor 5 is heated by means of a reactor heater 6 to atemperature of between 800° C. and 1100° C., so that a reaction betweenthe halogenated waste materials and the metal oxide-containing materialstakes place in the reactor. The products formed are separated in asolids trap 7, and the solid metal chlorides formed, in particular AlCl₃and FeCl₃, are discharged via a line 8. The remaining gases are purifiedby an activated carbon filter 9 and then compressed by a fan 10. Thegases are then cooled in a cooling tank 12, which comprises a coolantinlet 11 and a coolant outlet 13, so that the remaining metal chloridesare separated out. SiCl₄ is mainly involved here.

[0042] The gases are then fed to a condenser 15 and subjected to analkaline gas scrubbing in a gas scrubbing column 16. The column 16possesses a circulating pump 17 for the scrubbing fluid. The remainingsynthesis gas, a mixture of CO and H₂, is discharged through the line 18in the upper part of the gas scrubbing column 16.

[0043] The disposal of perchloroethylene (C₂Cl₄) and vinyl chloride(C₂H₃Cl, a monomer of polyvinyl chloride) as halogenated waste materialsmay be cited as an example of practical application. The conversiontakes place with slate wastes from slate production as the metaloxide-containing product.

[0044] Table 1: Slate analysis from Martelange, Belgian-Luxembourgborder region Compound Share in percent (% w/w) SiO₂ 59.1 Al₂O₃ 19.8Fe₂O₃ 8.2 Na₂O 2.5 CaO 2.4 K₂O 3.3 MgO 3.2 FeS₂ 0.5 C 1

[0045] Prior to the processing the slate wastes are reduced in size bymeans of a jaw crusher. Mean grain sizes in the range from 3-8 mm areadvantageous.

APPLICATION EXAMPLE 1 Disposal of PER

[0046] The ground slate can be introduced into the reactor by injectiontogether with the fluidising gas carbon dioxide (CO₂). A further supplyof fluidising gas serves for the production and maintenance of thefluidised bed. An amount of about 20-27 m³ Of CO₂ is supplied per houras fluidising gas.

[0047] The temperature of the fluidising gas is with advantage broughtto about 500° C. Perch loroethylene (C₂Cl₄, PER) is used as thehalogenated waste product. The PER is introduced as a sort of aerosol bya fluidising gas sub-flow directly into the reaction zone of thereactor. The PER is there decomposed into its constituents. Thedifference between PER and other solvents is that no hydrogen atoms arepresent in the molecule. The formation of hydrochloric acid (HCI) istherefore not possible.

[0048] Chlorine gas (Cl₂) is nevertheless formed, which is anoutstanding chlorinating agent. The chlorine gas therefore reacts in thefluidised bed with the metal oxides of the slate to form metal chlorides(in general Me_(x)Cl_(y)). Thus aluminium chloride (AlCl₃),iron-III-chloride (FeCl₃) and silicon tetrachloride (SiCl₄) can beformed.

[0049] The elemental carbon (C) occurring during the thermaldecomposition of the chlorinated hydrocarbons reacts either with thefluidising gas (CO₂) or with the bound oxygen of the metal oxides withthe formation of carbon monoxide.

[0050] Reaction equation 3 describes the chlorination of silicon dioxidewith the formation of silicon tetrachloride and carbon monoxide.

SiO₂+C₂Cl₄═SiCl₄+2 CO

[0051] Reaction Equation 3

[0052] The following equation applies in general to the disposal of PERwith slate:

SiO₂+2Al₂O₃+2Fe₂O₃+7C₂Cl₄═SiCl₄+4 AlCl₃+4FeCl₃+14 CO

[0053] Reaction Equation 4

[0054] It becomes clear from reaction equation 4 that in addition tocarbon monoxide various metal chlorides are formed. All the materialsoccur in gaseous form, initially at temperatures of about 1000° C.Directly downstream of the reactor the gases cool down very rapidly toabout 800° C. due to the ambient air.

[0055] The use of separation units such as cyclones or activated carbonfilters enables metal chlorides occurring in dusty or crystalline form,but mainly aluminium chloride and iron chloride, to be separated fromthe process gas flow and retained. The gas flow, supported by a fan, isaspirated through the filters. The result of this is that a slightvacuum can be noticed already at the reactor outlet, which lies in therange from about 0.01 to 0.05 bar below standard pressure.

[0056] The residual gases contain gaseous silicon tetrachloride andcarbon monoxide. Since the silicon tetrachloride passes into the solidstate at temperatures below −68° C., the process gas has to be cooled totemperatures of about −50° C. This takes place by a pre-cooling withliquid nitrogen and a subsequent cooling by means of a low-temperaturemixture in a condensation column. The low-temperature mixture used is anacetone-dry ice mixture, which can generate temperatures down to notmore than −86° C.

[0057] The silicon tetrachloride present in gaseous form is deposited inthe condenser at the above-mentioned temperatures and is collected in astorage tank. The degree of purity of the condensed silicontetrachloride is about 96%. Any foreign substances present can beremoved by a subsequent fractionated distillation. The result of thepurification by distillation would be a silicon tetrachloride solutionwith a degree of purity of approx. 99%.

[0058] After the condensation the process gas is subjected to analkaline gas scrubbing with a 10% potassium hydroxide solution accordingto the counter-flow principle. The gas purified in this way thencontains only carbon monoxide.

APPLICATION EXAMPLE 2 Disposal of Vinyl Chloride

[0059] The process engineering layout of the plant corresponds to thelayout that has also been used for the disposal of perchloroethylene(PER). The underlying chemical reactions are described below.

[0060] During the reacting of vinyl chloride (C₂H₃Cl), as a monomer ofpolyvinyl chloride (PVC), with slate wastes the following chemicalreactions occur, for example:

SiO₂+4 C₂H₃Cl+6 CO₂═SiCl₄+6H₂+14 CO

[0061] Reaction Equation 5

Al₂O₃+6 C₂H₃Cl+9 CO₂═2 AlCl₃+9H₂+21 CO

[0062] Reaction Equation 6

Fe₂O₃+6C₂H₃Cl+9CO₂═2FeCl₃+9H₂+21 CO

[0063] Reaction Equation 7

[0064] There is therefore obtained as the total reaction equation:

SiO₂+Al₂O₃+Fe₂O₃+16 C₂H₃Cl+24 CO₂═SiCl₄+2 AlCl₃+2 FeCl₃+24H₂+56 CO

[0065] Reaction Equation 8

[0066] The process engineering separation of the aluminium and the ironchloride (AlCl₃, FeCl₃) takes place on the one hand by centrifugal forcedeposition in a cyclone and on the other by deposition in specialfilters. The separation of the silicon tetrachioride takes place in themanner already described.

[0067] It is obvious from reaction equation 8 that in addition to themetal chlorides a synthesis gas consisting of carbon monoxide andhydrogen is formed. The ratio between hydrogen and carbon monoxide is1:2.3. A so-called synthesis gas is spoken of here, which has manytechnical uses.

APPLICATION EXAMPLE 3 Disposal of Hydrocarbon- (HC) or HalogenatedHydrocarbon-Containing (HHC) Wastes in the Presence of Calcium Oxide

[0068] The various feedstocks, such as inter alia oils, fats, PCBs,CFCs, solvents or similar are conveyed via a metering device, e.g. aneccentric screw pump, into the reaction zone. There a first thermalcleavage of the feedstocks into short-chain hydrocarbons takes placevery rapidly. The residence time of the feedstocks or that of thecleavage products obtained is determined by the height of the reactionzone.

[0069] As a rule a virtually quantitative breakdown into substantiallyhydrogen and methane takes place, wherein the volume ratio of hydrogento methane lies clearly on the side of the hydrogen. Since the meltingpoint of calcium oxide (CaO) is around 2500° C., substantial amounts ofsynthesised calcium compounds do not have to be allowed for.

[0070] If on the other hand halogenated feedstocks, in particularchlorinated materials, are caused to react, a reaction between thecalcium oxide and the halogen atoms of the feedstocks then occurs.

[0071] In the main calcium chloride (CaCl₂) is formed as the reactionproduct, which remains in the reactor as slag or melt. The followingreaction equation (reaction equation 1) takes account of all the mainproducts which are formed during the disposal or recycling of ahalogenated hydrocarbon. The individual products have been calculatedthermodynamically and attested experimentally.

2 CaO+4 C₂H₅Cl═2 CaCl₂+2 CO+CH₄+5 C+8H₂

[0072] Reaction Equation 9

[0073] In addition to this reaction, carbon in the form of fine sootparticles is also discharged out of the reactor.

[0074] The separation from the remaining gaseous constituents hydrogenand methane, or hydrogen and carbon monoxide (CO), is carried out bygravity separators, such as a high-capacity cyclone.

[0075] The gases cleaned in this way can in the interests of safety alsobe passed through activated carbon filters. Should foreign constituentsstill be contained in the process gas, the latter can be removed eitherby targeted condensation or by a gas scrubbing.

[0076] Finally, there remains as a rule only one synthesis gas,consisting of carbon monoxide, methane and hydrogen, which can be usedfor many different technical applications, e.g. energy recovery or usefor chemical syntheses (methanol synthesis).

1. Process for disposing of halogenated and non-halogenated wastematerials, characterised in that the waste materials are reacted withmetal-oxide containing products with the exclusion of oxygen attemperatures of 800° C. to 1100° C.
 2. Process according to claim 1,characterised in that the waste materials contain carbon.
 3. Processaccording to claim 1 or 2, characterised in that carbon dioxide is addedduring the process.
 4. Process according to any one of the previousclaims, characterised in that carbon is added during the process. 5.Process according to claim 4, characterised in that graphite and/or coalis used as carbon.
 6. Process according to any one of the previousclaims, characterised in that halogenatable metal oxide-containingproducts are used as a metal oxide-containing educt.
 7. Processaccording to claim 6, characterised in that products which contain TiO₂,SiO₂, Al₂O₃, CaO and/or Fe₂O₃ or a mixture thereof are used ashalogenatable metal oxide-containing materials.
 8. Process according toany one of the preceding claims, characterised in that solvents such ascarbon tetrachloride, chloroform, methylene chloride, tetra- andtrichloroethylene, tetrachloroethane, coolants or refrigerants, PCB,pesticides, fungicides and herbicides, halogenated plastics such as PVCare used as halogenated waste materials.
 9. Process according to any oneof the preceding claims, characterised in that a portion of the metaloxide that corresponds to the chlorine content of the waste materials isconverted into metal chloride.
 10. Process according to any one ofclaims 1 to 7, characterised in that spent oils, lubricants, fats,paints, dyes, tars, waxes, plastics, coolants and solvents, brake fluidor similar non-halogenated substances and materials are used asnon-halogenated waste materials.